Sites providing Online Courses :

edX : This site is great source for free online courses. All courses are freely available. You have to pay minimum fees for course only if you require a Verified Certificate of Achievement to document your accomplishment, which is useful for job applications, career advancement, or school applications. This site contains more than 400 online courses from many different domains or subjects like Art, Education, Computer Science and many more. Find your favorite one right now from here. You will find leading global universities like MIT, Harvard, Berkeley, IIT Bombay and many more in consortium of edX.

udacity : It also contains many courses but most of them on trial basis for some days and then you have to pay if you wish to continue. The good thing with udacity is that, you find categorization of courses in levels as :

• New to Tech

• Beginner

• Intermediate

• Advance

which helps you to choose correct course. Like edX you can sign up here by using your google or facebook account. 

ureddit : This is another better option to take online courses. Content on the site is totally free. Also courses are well categorized like Art, computer sciences, technology and many more. You can view current classes as well as archived classes. One of the added advantage of ureddit is that you can easily add your own classes by just sign up. 

coursera : This site have organized different courses according to specialization. Courses on this site are not freely available. You will get signature certificate after successful completion of the course.